I need help with promotional issue.

My oldest daughter decided a few months back that she would get off momma and daddy's bill and go out on her own. We had five lines including hers and were with Sprint which we hated. She checked with AT&T in Fayetteville, NC where she goes to school and the sales person she talked to told her about the promotion that offered up to $650 per line towards the previous carriers charges in addition to receiving credit for her old phone. She specifically asked if all charges would be covered with Sprint and she was told yes.

My husband and I still had both of our lines, plus two more children with Sprint. We hated the service with them, so we went a few weeks later to speak to a sales person in Monroe, NC to find out what promotions they were offering because if we could get out from under Sprint we wanted to, but we did not want to be stuck owing them a lot of money. The gentleman I spoke to was very nice and helpful and informed me of the same promotion offered to my daughter of $650 per line in addition to credit for our old phones being traded in. I discussed at great length with him how I did not want to owe Sprint money by switching to AT&T, because we would deal with bad service until July if that was the case. He told me that the money would be more than enough to pay off each of our old phones since most companies don't place you in a contract anymore. We signed up that night and switched back to AT&T. While we were there, my middle daughter's fiance, picked her up on his bill. He was already with AT&T. Even though we were down to 3 people, our bill was just as high as it had been at Sprint when we had 5 people, but we were willing to do that if it meant having better service. 

While we were there, we were told that we had to trade in our phones in order to get the $650 promotion, so we all traded in our cell phones and we were told that we had a credit because of the phone trade in and could buy cases and screen protectors with that credit, so that's what we did, excited to not have to pay anything out of pocket.

We turned in our last phone bill from Sprint, to AT&T so that they could process the reimbursements for the balance owed to Sprint on our old devices. However, the problem is that when we received reimbursement from AT&T the amount of store credit we had used to purchase cases and screen protectors was deducted from the amount we were told we would receive. If I trade in my phone and I get a store credit, that makes sense; it's a wash. However, to then deduct that money from the reimbursement I received, is like me giving my phone to AT&T for nothing. The phone trade-in should have covered what I bought in store. At no point was it ever communicated to me at the store in Monroe, NC nor was it communicated to my daughter in the store in Fayetteville, NC that we would be lose that money on the reimbursement. I even went back the next day to switch my son because he wasn't with us the night before, and spoke to a different sales person. She never told me this either. It was the same spill about how we would receive up to $650 per line and charges would be covered. I am now left owing Sprint just over $600 because of this and I would have never switched until July when our phones would have been paid off had I known. I would love to be able to speak with someone who could help me get this resolved.